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Manipulating Strings in PHP Programming

Learn how to construct, compare, and manipulate text strings in PHP programming, including working with single and multiple strings, parsing strings, using regular expressions, and modifying string case.

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Manipulating Strings in PHP Programming

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  1. Chapter 3Manipulating StringsPHP Programming with MySQL2nd Edition

  2. Objectives In this chapter, you will: • Construct text strings • Work with single strings • Work with multiple strings and parse strings • Compare strings • Use regular expressions PHP Programming with MySQL, 2nd Edition

  3. Constructing Text Strings • A text string contains zero or more characters surrounded by double or single quotation marks • Text strings can be used as literal values or assigned to a variable echo "<PHP literal text string</p>"; $StringVariable = "<p>PHP literal text string</p>"; echo $StringVariable; • A string must begin and end with a matching quotation mark (single or double) PHP Programming with MySQL, 2nd Edition

  4. Constructing Text Strings (continued) • To include a quoted string within a literal string surrounded by double quotation marks, you surround the quoted string with single quotation marks • To include a quoted string within a literal string surrounded by single quotation marks, you surround the quoted string with double quotation marks PHP Programming with MySQL, 2nd Edition

  5. Constructing Text Strings (continued) $LatinQuote = '<p>"Et tu, Brute!"</p>'; echo $LatinQuote; Figure 3-2 Output of a text string containing double quotation marks PHP Programming with MySQL, 2nd Edition

  6. Working with String Operators In PHP, you use two operators to combine strings: • Concatenation operator (.) combines two strings and assigns the new value to a variable $City = "Paris"; $Country = "France"; $Destination = <p>“ . $City . " is in " . $Country . ".</p>"; echo $Destination; PHP Programming with MySQL, 2nd Edition

  7. Working with String Operators (continued) • You can also combine strings using the concatenation assignment operator (.=) $Destination = "<p>Paris"; $Destination .= "is in France.</p>"; echo $Destination; PHP Programming with MySQL, 2nd Edition

  8. Adding Escape Characters and Sequences • An escape character tells the compiler or interpreter that the character that follows it has a special purpose • In PHP, the escape character is the backslash (\) echo '<p>This code\'s going to work</p>'; • Do not add a backslash before an apostrophe if you surround the text string with double quotation marks echo "<p>This code's going to work.</p>"; PHP Programming with MySQL, 2nd Edition

  9. Adding Escape Characters and Sequences (continued) • The escape character combined with one or more other characters is an escape sequence PHP Programming with MySQL, 2nd Edition

  10. Adding Escape Characters and Sequences (continued) $Speaker = "Julius Caesar"; echo "<p>\"Et tu, Brute!\" exclaimed $Speaker.</p>"; Figure 3-4 Output of literal text containing double quotation escape sequences PHP Programming with MySQL, 2nd Edition

  11. Simple and Complex String Syntax • Simple string syntax uses the value of a variable within a string by including the variable name inside a text string with double quotation marks $Vegetable = "broccoli"; echo "<p>Do you have any $Vegetable?</p>"; • When variables are placed within curly braces inside of a string, it is called complex string syntax $Vegetable = "carrot"; echo "<p>Do you have any {$Vegetable}s?</p>"; PHP Programming with MySQL, 2nd Edition

  12. Working with a Single String • PHP provides a number of functions for analyzing, altering, and parsing text strings including: • Counting characters and words • Transposing, converting, and changing the case of text within a string PHP Programming with MySQL, 2nd Edition

  13. Counting Characters and Words in a String • The most commonly used string counting function is the strlen() function, which returns the total number of characters in a string • Escape sequences, such as \n, are counted as one character $BookTitle = "The Cask of Amontillado"; echo "<p>The book title contains " . strlen($BookTitle) . " characters.</p>"; PHP Programming with MySQL, 2nd Edition

  14. Counting Characters and Words in a String (continued) • The str_word_count() function returns the number of words in a string • Pass the str_word_count() function a literal string or the name of a string variable whose words you want to count $BookTitle = "The Cask of Amontillado"; echo "<p>The book title contains " .str_word_count($BookTitle). " words.</p>"; PHP Programming with MySQL, 2nd Edition

  15. Modifying the Case of a String • PHP provides several functions to manipulate the case of a string • The strtoupper()function converts all letters in a string to uppercase • The strtolower()function converts all letters in a string to lowercase • The ucfirst()function ensures that the first character of a word is uppercase • The lcfirst()function ensures that the first character of a word is lowercase PHP Programming with MySQL, 2nd Edition

  16. Modifying the Case of a String(continued) • Functions to manipulate the case of a string: • The ucwords()function changes the first character of each word • Use the strtolower()function on a string before using the ucfirst()and ucwords() to ensure that the remaining characters in a string are in lowercase • Use the strtoupper()function on a string before using the ucfirst() and ucwords() to ensure that the remaining characters in a string are in uppercase PHP Programming with MySQL, 2nd Edition

  17. Encoding and Decoding a String • PHP has several built-in functions to use with Web pages: • Some characters in XHTML have a special meaning and must be encoded using HTML entities in order to preserve that meaning • The htmlspecialchars()function converts special characters to HTML entities • The html_specialcharacters_decode() function converts HTML character entities into their equivalent characters PHP Programming with MySQL, 2nd Edition

  18. Encoding and Decoding a String(continued) • The characters that are converted with the htmlspecialchars()function are: • '&' (ampersand) becomes '&amp;' • '"' (double quote) becomes '&quot;' when ENT_NOQUOTES is disabled. • ''' (single quote) becomes '&#039;' only when ENT_QUOTES is enabled. • '<' (less than) becomes '&lt;' • '>' (greater than) becomes '&gt;' PHP Programming with MySQL, 2nd Edition

  19. Encoding and Decoding a String(continued) • If ENT_QUOTES is enabled in the PHP configuration, both single and double quotes are converted • If ENT_QUOTES is disabled in the PHP configuration, neither single nor double quotes are converted PHP Programming with MySQL, 2nd Edition

  20. Encoding and Decoding a String(continued) • The md5()function uses a strong encryption algorithm (called the Message-Digest Algorithm) to create a one-way hash • A one-way hash is a fixed-length string based on the entered text, from which it is nearly impossible to determine the original text • The md5() function does not have an equivalent decode function, which makes it a useful function for storing passwords in a database PHP Programming with MySQL, 2nd Edition

  21. Other Ways to Manipulate a String • PHP provides three functions that remove leading or trailing spaces in a string • The trim()function will strip (remove) leading or trailing spaces in a string • The ltrim() function removes only the leading spaces • The rtrim() function removes only the trailing spaces PHP Programming with MySQL, 2nd Edition

  22. Other Ways to Manipulate a String (continued) • The substr()function returns part of a string based on the values of the start and length parameters • The syntax for the substr() function is: substr(string, start, optional length); • A positive number in the startparameter indicates how many character to skip at the beginning of the string • A negative number in the start parameter indicates how many characters to count in from the end of the string PHP Programming with MySQL, 2nd Edition

  23. Other Ways to Manipulate a String(continued) • A positive value in the in the length parameter determines how many characters to return • A negative value in the length parameter skip that many characters at the end of the string and returns the middle portion • If the length is omitted or is greater than the remaining length of the string, the entire remainder of the string is returned PHP Programming with MySQL, 2nd Edition

  24. Other Ways to Manipulate a String(continued) $ExampleString = "woodworking project"; echo substr($ExampleString,4) . "<br />\n"; echo substr($ExampleString,4,7) . "<br />\n"; echo substr($ExampleString,0,8) . "<br />\n"; echo substr($ExampleString,-7) . "<br />\n"; echo substr($ExampleString,-12,4) . "<br />\n"; Figure 3-10 Some examples using the substr() function PHP Programming with MySQL, 2nd Edition

  25. Working with Multiple Strings • Parsing is the act of dividing a string into logical component substrings or tokens • When programming, parsing refers to the extraction of information from string literals and variables PHP Programming with MySQL, 2nd Edition

  26. Finding and Extracting Characters and Substrings • There are two types of string search and extraction functions: • Functions that return a numeric position in a text string • Functions that return a character or substring • Both functions return a value of FALSE if the search string is not found PHP Programming with MySQL, 2nd Edition

  27. Finding and Extracting Characters and Substrings (continued) • The strpos() function performs a case-sensitive search and returns the position of the first occurrence of one string in another string • Pass two arguments to the strpos() function: • The first argument is the string you want to search • The second argument contains the characters for which you want to search • If the search string is not found, the strpos() function returns a Boolean value of FALSE PHP Programming with MySQL, 2nd Edition

  28. Finding and Extracting Characters and Substrings (continued) • Pass to the strchr() and the strrchr() functions the string and the character for which you want to search • Both functions return a substring from the specified characters to the end of the string • strchr() function starts searching at the beginning of a string • strrchr() function starts searching at the end of a string PHP Programming with MySQL, 2nd Edition

  29. Replacing Characters and Substrings • The str_replace() and str_ireplace() functions both accept three arguments: • The string you want to search for • A replacement string • The string in which you want to replace characters $Email = "president@whitehouse.gov"; $NewEmail = str_replace("president", "vice.president", $Email); echo $NewEmail; // prints 'vice.president@whitehouse.gov' PHP Programming with MySQL, 2nd Edition

  30. Dividing Strings into Smaller Pieces • Use the strtok() function to break a string into smaller strings, called tokens • The syntax for the strtok()function is: $variable = strtok(string, separators); • The strtok() function returns the entire string if: • An empty string is specified as the second argument of the strtok() function • The string does not contain any of the separators specified PHP Programming with MySQL, 2nd Edition

  31. Dividing Strings into Smaller Pieces (continued) $Presidents = " George Washington;John Thomas Jefferson;James Madison;James Monroe"; $President = strtok($Presidents, ";"); while ($President != NULL) { echo "$President<br />"; $President = strtok(";"); } Figure 3-15 Output of a script that uses the strtok() function PHP Programming with MySQL, 2nd Edition

  32. Dividing Strings into Smaller Pieces(continued) $Presidents = " George Washington;John Adams;Thomas Jefferson;James Madison;James Monroe"; $President = strtok($Presidents, "; "); while ($President != NULL) { echo "$President<br />"; $President = strtok("; "); } Figure 3-16 Output of a script with a strtok() function that uses two separators PHP Programming with MySQL, 2nd Edition

  33. Converting between Strings and Arrays • The str_split() and explode() functions split a string into an indexed array • The str_split() function splits each character in a string into an array element using the syntax: $array = str_split(string[, length]); • The lengthargument represents the number of characters you want assigned to each array element PHP Programming with MySQL, 2nd Edition

  34. Converting between Strings and Arrays (continued) • The explode() function splits a string into an indexed array at a specified separator • The syntax for the explode() function is: $array = explode(separators, string); • The order of the arguments for the explode() function is the reverse of the arguments for the strtok() function PHP Programming with MySQL, 2nd Edition

  35. Converting between Strings and Arrays (continued) $Presidents = "George Washington;JohnAdams; Thomas Jefferson;James Madison;James Monroe"; $PresidentArray = explode(";", $Presidents); foreach ($PresidentArray as $President) { echo "$President<br />"; } • If the string does not contain the specified separators, the entire string is assigned to the first element of the array PHP Programming with MySQL, 2nd Edition

  36. Converting between Strings and Arrays (continued) • The explode() function • Does not separate a string at each character that is included in the separator argument • Evaluates the characters in the separator argument as a substring • If you pass to the explode()function an empty string as the separator argument, the function returns a Boolean value of FALSE PHP Programming with MySQL, 2nd Edition

  37. Converting between Strings and Arrays (continued) • The implode()function combines an array’s elements into a single string, separated by specified characters • The syntax is: $variable = implode(separators, array); PHP Programming with MySQL, 2nd Edition

  38. Converting between Strings and Arrays (continued) $PresidentsArray = array("George Washington", “John Adams", “Thomas Jefferson", “James Madison", “James Monroe"); $Presidents = implode(", ", $PresidentsArray); echo $Presidents; Figure 3-18 Output of a string created with the implode() function PHP Programming with MySQL, 2nd Edition

  39. Comparing Strings • Comparison operators compare individual characters by their position in the American Standard Code for Information Interchange (ASCII), which are numeric representations of English characters $FirstLetter = "A"; $SecondLetter = "B"; if ($SecondLetter > $FirstLetter) echo "<p>The second letter is higher in the alphabet than the first letter.</p>"; else echo "<p>The second letter is lower in the alphabet than The first letter.</p>"; PHP Programming with MySQL, 2nd Edition

  40. Comparing Strings (continued) • American Standard Code for Information Interchange (ASCII) values range from 0 to 255 • Lowercase letters are represented by the values 97 (“a”) to 122 (“z”) • Uppercase letters are represented by the values 65 (“A”) to 90 (“Z”) PHP Programming with MySQL, 2nd Edition

  41. String Comparison Functions • The strcasecmp() function performs a case-insensitive comparison of strings • The strcmp() function performs a case-sensitive comparison of strings • Both functions accept two arguments representing the strings you want to compare • Most string comparison functions compare strings based on their ASCII values PHP Programming with MySQL, 2nd Edition

  42. Determining the Similarity of Two Strings • The similar_text() and levenshtein() functions are used to determine the similarity between two strings • The similar_text() function returns the number of characters that two strings have in common • The levenshtein() function returns the number of characters you need to change for two strings to be the same PHP Programming with MySQL, 2nd Edition

  43. Determining the Similarity of Two Strings (continued) • Both functions accept two string arguments representing the values you want to compare $FirstName = "Don"; $SecondName = "Dan"; echo "<p>The names \"$FirstName\“ and \"$SecondName\“ have “ . similar_text($FirstName, $SecondName) . “ characters in common.</p>"; echo "<p>You must change “ . levenshtein($FirstName, $SecondName) . “ character(s) to make the names \"$FirstName\“ and \"$SecondName\“ the same.</p>"; PHP Programming with MySQL, 2nd Edition

  44. Determining the Similarity of Two Strings (continued) Figure 3-20 Output of a script with the similar_text() and levenshtein() functions PHP Programming with MySQL, 2nd Edition

  45. Determining if Words are Pronounced Similarly • The soundex() and metaphone() functions determine whether two strings are pronounced similarly • Both functions return a value representing how words sound • The soundex() function returns a value representing a name’s phonetic equivalent • The metaphone() function returns a code representing an English word’s approximate sound PHP Programming with MySQL, 2nd Edition

  46. Determining if Words are Pronounced Similarly (continued) $FirstName = "Gosselin"; $SecondName = "Gauselin"; $FirstNameSoundsLike = metaphone($FirstName); $SecondNameSoundsLike = metaphone($SecondName); if ($FirstNameSoundsLike == $SecondNameSoundsLike) echo "<p>The names are pronounced the same.</p>"; else echo "<p>The names are not pronounced the same.</p>"; PHP Programming with MySQL, 2nd Edition

  47. Working with Regular Expressions • Regular Expressions are patterns that are used for matching and manipulating strings according to specified rules • PHP supports two types of regular expressions: • POSIX Extended • Perl Compatible Regular Expressions PHP Programming with MySQL, 2nd Edition

  48. Working with Regular Expressions(continued) PHP Programming with MySQL, 2nd Edition

  49. Working with Regular Expressions(continued) • Pass to the preg_match() the regular expression pattern as the first argument and a string containing the text you want to search as the second argument preg_match(pattern, string); PHP Programming with MySQL, 2nd Edition

  50. Writing Regular Expression Patterns • A regular expression pattern is a special text string that describes a search pattern • Regular expression patterns consist of literal characters and metacharacters, which are special characters that define the pattern-matching rules • Regular expression patterns are enclosed in opening and closing delimiters • The most common character delimiter is the forward slash (/) PHP Programming with MySQL, 2nd Edition

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